Independently routable digital subcarriers for optical communication networks

ABSTRACT

Optical network systems and components are disclosed including a transmitter comprising a digital signal processor receiving a plurality of independent data streams, the digital signal processor supplying outputs based on the plurality of independent data streams, the digital signal processor comprising a plurality of pulse shape filters corresponding to the plurality of independent data streams, the plurality of pulse shape filters configured to filter the independent data streams to produce a first subcarrier having a first frequency bandwidth and a second subcarrier having a second frequency bandwidth different than the first frequency bandwidth for the outputs.

INCORPORATION BY REFERENCE

The entirety of the following patents and patent applications are herebyexpressly incorporated herein by reference: U.S. Pat. No. 8,831,439,entitled “Upsampling Optical Transmitter”, which issued Sep. 9, 2014;U.S. Pat. No. 10,014,975, entitled “Channel Carrying Multiple DigitalSubcarriers”, which issued Jul. 3, 2018; U.S. patent application Ser.No. 16/155,624, entitled “Individually Routable Digital Subcarriers”,which was filed Oct. 9, 2018; U.S. Provisional Patent Application No.62/627,712, entitled “Independently Routable Digital Subcarriers forOptical Network”, which was filed Feb. 7, 2018, to which the presentapplication claims priority; and Provisional Patent Application No.62/668,297, entitled “Spectral Efficiency Improvements using VariableSubcarrier Root-Raised Cosine Shaping”, which was filed May 8, 2018, towhich the present application claims priority.

FIELD OF THE DISCLOSURE

The disclosure generally relates to methods and apparatuses for thegeneration and use of subcarriers in optical communication systems. Moreparticularly the disclosure relates to such methods and apparatuses thatroute or direct individual subcarriers to a different destination,wherein the modulation format, data rate, and/or baud rate, as well asthe spectral width and frequency spacing between subcarriers, may betailored for each subcarrier based on receiver characteristics and/or inaccordance with the path or route over which a corresponding subcarrieris transmitted.

BACKGROUND

Communication systems are known in which optical signals, each beingmodulated to carry data and having a different wavelength, aretransmitted from a first location to a second location. The opticalsignals may be combined on a single fiber and transmitted to a receivingnode that includes circuitry to optically separate or demultiplex eachsignal. Alternatively, coherent detection techniques may be employed toextract the data carried by each optical signal.

In such systems, a plurality of transmitters may be provided, such thateach transmitter supplies a respective one of the optical signals.Typically, each transmitter includes a laser, modulator, and associatedcircuitry for controlling the modulator and the laser. As networkcapacity requirements increase, however, additional transmitters may beprovided to supply additional optical signals, but at significantlyincreased cost.

Moreover, communications systems may include multiple nodes, such thatselected optical signals may be intended to transmission to certainnodes, and other signals may be intended for reception by one or moreother nodes. Accordingly, optical add-drop multiplexers (“OADMs”) may beprovided to drop one or more signals at an intended local receiver, forexample, while other optical signals are passed by the OADM to one ormore downstream nodes. Further, optical signals may be added by the OADMfor transmission to one or more nodes in the communication system. Thus,the optical signals may be transmitted over varying distances andthrough varying numbers of OADMs. In addition, the data and/or baudrate, and or modulation format is preferably tailored to a particularroute, as well as the capacity of the intended receiver.

Thus, not only may multiple transmitters be required to provide arequired number of optical signals to satisfy network capacity needs,but each transmitter may be required to be customized to generate eachoptical signal with a desired modulation format, data rate, and/or baudrate.

SUMMARY

Optical communication network systems and methods are disclosed. Theproblem of requiring multiple transmitters to provide a required numberof optical signals to satisfy network capacity needs, and requiring eachtransmitter to be customized to generate each optical signal with adesired modulation format, data rate, and/or baud rate is addressedthrough systems and methods for providing subcarriers that may be routedthrough a network independently of one another. In addition, eachsubcarrier may have characteristics, such as baud rate, data rate andmodulation format, spectral width, and frequency spacings that may betailored based on the intended receiver for such subcarrier and theparticular optical path or route over which the subcarrier istransmitted.

Consistent with an aspect of the present disclosure, a transmitter maycomprise a digital signal processor receiving a plurality of independentdata streams, the digital signal processor supplying outputs based onthe plurality of independent data streams, the digital signal processorcomprising a plurality of pulse shape filters corresponding to theplurality of independent data streams, the plurality of pulse shapefilters configured to filter the independent data streams to produce afirst subcarrier having a first frequency bandwidth and a secondsubcarrier having a second frequency bandwidth different than the firstfrequency bandwidth for the outputs; one or more digital-to-analogconverter configured to convert the outputs of the digital signalprocessor to voltage signal outputs; a laser configured to output anoptical light beam; and a modulator configured to modulate the opticallight beam, based on the voltage signal outputs, to output a modulatedoptical signal including a plurality of optical subcarriers based on theoutputs of the digital signal processor, wherein a first one of theplurality of optical subcarriers carries data indicative of a first oneof the plurality of independent data streams, and a second one of theplurality of optical subcarriers carries data indicative of a second oneof the plurality of independent data streams, and wherein the first oneof the plurality of optical subcarriers has a first bandwidth and thesecond one of the plurality of optical subcarriers has a secondbandwidth different than the first bandwidth.

In one implementation, the plurality of optical subcarriers are Nyquistoptical subcarriers.

In one implementation, the number of the plurality of opticalsubcarriers may be greater than the number of the plurality ofindependent data streams and two or more of the plurality of opticalsubcarriers may carry a single one of the plurality of independent datastreams.

In some implementations, the optical subcarriers may carry data with adifferent symbol rates, may have different data capacity, may havevariable spacing between the optical subcarriers, may have differentbandwidths, may carry clock recovery information in one opticalsubcarrier for multiple subcarriers, and/or may be modulated inaccordance with the same or different modulation formats

Consistent with an aspect of the present disclosure, a receiver maycomprise circuitry configured to receive a plurality of opticalsubcarriers, each of which carrying data indicative of a respective oneof a plurality of independent data streams, the plurality of opticalsubcarriers comprising a first subcarrier having a first bandwidth and asecond subcarrier having a second bandwidth larger than the firstbandwidth, and to convert the plurality of optical subcarriers intodigital signals. Optionally, the receiver may further comprise a digitalsignal processor configured to receive the digital signals from thecircuitry and recover clock information for the plurality of opticalsubcarriers from the second one of the optical subcarriers. Theplurality of optical subcarriers may be Nyquist optical subcarriers.

Consistent with an aspect of the present disclosure, an optical networkmay comprise a transmitter, comprising a digital signal processorreceiving a plurality of independent data streams, the digital signalprocessor supplying outputs based on the plurality of independent datastreams, the digital signal processor comprising a plurality of pulseshape filters corresponding to the plurality of independent datastreams, the plurality of pulse shape filters configured to filter theindependent data streams to produce a first subcarrier having a firstfrequency bandwidth and a second subcarrier having a second frequencybandwidth different than the first frequency bandwidth for the outputs;one or more digital-to-analog converter configured to convert theoutputs of the digital signal processor to voltage signal outputs; alaser configured to output an optical light beam; and a modulatorconfigured to modulate the optical light beam, based on the voltagesignal outputs, to output a modulated optical signal including aplurality of optical subcarriers based on the outputs of the digitalsignal processor, wherein a first one of the plurality of opticalsubcarriers carries data indicative of a first one of the plurality ofindependent data streams, and a second one of the plurality of opticalsubcarriers carries data indicative of a second one of the plurality ofindependent data streams, and wherein the first one of the plurality ofoptical subcarriers has a first bandwidth and the second one of theplurality of optical subcarriers has a second bandwidth different thanthe first bandwidth. The optical network may further comprise areceiver, comprising circuitry configured to receive the plurality ofoptical subcarriers; and a digital signal processor configured toconvert one or more of the plurality of optical subcarriers to outputone or more of the plurality of independent data streams.

The optical network of claim 18 may further comprise one or more opticaladd-drop multiplexer (OADM) configured to do one or more of: drop one ormore of the optical subcarriers from the modulated optical signal fromthe transmitter and add one or more optical subcarrier to the modulatedoptical signal from the transmitter.

Consistent with an aspect of the present disclosure, a transmitter maycomprise a digital signal processor receiving a plurality of independentdata streams, the digital signal processor supplying outputs based onthe plurality of independent data streams; one or more digital-to-analogconverter configured to convert the outputs of the digital signalprocessor to voltage signal outputs; a laser configured to output anoptical light beam; and a modulator configured to modulate the opticallight beam, based on the voltage signal outputs, to output a modulatedoptical signal including a plurality of optical subcarriers based on theoutputs of the digital signal processor, wherein a first one of theplurality of optical subcarriers carries data indicative of a first oneof the plurality of independent data streams, and a second one and athird one of the plurality of optical subcarriers carries dataindicative of a second one of the plurality of independent data streams,such that a number of the plurality of optical subcarriers is greaterthan the number of the plurality of independent data streams.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate one or more implementationsdescribed herein and, together with the description, explain theseimplementations. In the drawings:

FIG. 1 illustrates an optical communication system consistent with anaspect of the present disclosure;

FIG. 2 is a diagram illustrating an example of components of an opticaltransmitter shown in FIG. 1;

FIG. 3 is a diagram illustrating example components of a transmitterdigital signal processor (Tx DSP) shown in FIG. 2;

FIG. 4A illustrates an exemplary plurality of subcarriers consistentwith an aspect of the present disclosure;

FIG. 4B illustrates another exemplary plurality of subcarriersconsistent with an aspect of the present disclosure;

FIG. 4C illustrates another exemplary plurality of subcarriersconsistent with an aspect of the present disclosure;

FIG. 4D illustrates another exemplary plurality of subcarriersconsistent with an aspect of the present disclosure;

FIG. 4E illustrates another exemplary plurality of subcarriersconsistent with an aspect of the present disclosure;

FIG. 5A is a diagram illustrating a portion of an exemplary processconsistent with an aspect of the present disclosure;

FIG. 5B is a diagram illustrating a portion of another exemplary processconsistent with an aspect of the present disclosure;

FIG. 5C is a diagram illustrating exemplary variable-spaced subcarriersconsistent with an aspect of the present disclosure;

FIG. 5D is a diagram illustrating exemplary variable-spaced subcarriersconsistent with an aspect of the present disclosure;

FIG. 5E is a diagram illustrating an exemplary subcarrier consistentwith an aspect of the present disclosure;

FIG. 6 is a diagram illustrating an example of components of an opticalreceiver shown in FIG. 1 consistent with an aspect of the presentdisclosure;

FIG. 7 is a diagram illustrating example components of an exemplaryreceiver digital signal processor (Rx DSP), such as that shown in FIG.6, consistent with an aspect of the present disclosure;

FIG. 8A is an illustration of a use case example of subcarriers havingfixed subcarrier width and variable capacity per subcarrier consistentwith an aspect of the present disclosure;

FIG. 8B is an illustration of another use case example of subcarriershaving fixed subcarrier width and variable capacity per subcarrierconsistent with an aspect of the present disclosure;

FIG. 8C is an illustration of another use case example of subcarriershaving fixed subcarrier width and variable capacity per subcarrierconsistent with an aspect of the present disclosure;

FIG. 8D is an illustration of another use case example of subcarriershaving fixed subcarrier width and variable capacity per subcarrierconsistent with an aspect of the present disclosure;

FIG. 8E is an illustration of another use case example of subcarriershaving fixed subcarrier width and variable capacity per subcarrierconsistent with an aspect of the present disclosure;

FIG. 8F is an illustration of another use case example of subcarriershaving fixed subcarrier width and variable capacity per subcarrierconsistent with an aspect of the present disclosure;

FIG. 8G is an illustration of another use case example of subcarriershaving fixed subcarrier width and variable capacity per subcarrierconsistent with an aspect of the present disclosure;

FIG. 9A is an illustration of a use case example of subcarriers havingfixed capacity and variable subcarrier width consistent with an aspectof the present disclosure;

FIG. 9B is an illustration of another use case example of subcarriershaving fixed capacity and variable subcarrier width consistent with anaspect of the present disclosure;

FIG. 9C is an illustration of another use case example of subcarriershaving fixed capacity and variable subcarrier width consistent with anaspect of the present disclosure;

FIG. 9D is an illustration of another use case example of subcarriershaving fixed capacity and variable subcarrier width consistent with anaspect of the present disclosure;

FIG. 10 illustrates an exemplary mesh network configuration consistentwith a further aspect of the present disclosure;

FIG. 11A illustrates an exemplary ring network configuration consistentwith a further aspect of the present disclosure;

FIG. 11B illustrates exemplary components of a node of the network ofFIG. 11A consistent with a further aspect of the present disclosure;

FIG. 12A illustrates an exemplary network configuration consistent witha further aspect of the present disclosure;

FIG. 12B illustrates another exemplary network configuration consistentwith a further aspect of the present disclosure;

FIG. 13 illustrates an exemplary ring and hub network configurationconsistent with a further aspect of the present disclosure.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawings.The same reference numbers in different drawings may identify the sameor similar elements.

The mechanisms proposed in this disclosure circumvent the problemsdescribed above. The present disclosure describes a system and/orcomponents that route or direct individual subcarriers to a differentdestination, wherein the modulation format, data rate, and/or baud rate,as well as the spectral width and frequency spacing between subcarriers,may be tailored for each subcarrier based on receiver characteristicsand/or in accordance with the path or route over which a correspondingsubcarrier is transmitted.

DEFINITIONS

If used throughout the description and the drawings, the following shortterms have the following meanings unless otherwise stated:

ADC stands for analog-to-digital converter.

DAC stands for digital-to-analog converter.

DSP stands for digital signal processor.

OADM stands for optical add-drop multiplexer.

PIC stands for photonic integrated circuit.

Rx (or RX) stands for Receiver, which typically refers to opticalchannel receivers, but can also refer to circuit receivers.

Tx (or TX) stands for Transmitter, which typically refers to opticalchannel transmitters, but can also refer to circuit transmitters.

DESCRIPTION

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition A or B is satisfied by anyone of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

In addition, use of the “a” or “an” are employed to describe elementsand components of the embodiments herein. This is done merely forconvenience and to give a general sense of the inventive concept. Thisdescription should be read to include one or more and the singular alsoincludes the plural unless it is obvious that it is meant otherwise.

Further, use of the term “plurality” is meant to convey “more than one”unless expressly stated to the contrary.

Further, the phrase “based on” is intended to mean “based, at least inpart, on” unless explicitly stated otherwise.

Also, certain portions of the implementations have been described as“components” or “circuitry” that perform one or more functions. The term“component” or “circuitry” may include hardware, such as a processor, anapplication specific integrated circuit (ASIC), or a field programmablegate array (FPGA), or a combination of hardware and software. Softwareincludes one or more computer executable instructions that when executedby one or more component cause the component or circuitry to perform aspecified function. It should be understood that the algorithmsdescribed herein are stored on one or more non-transient memory.Exemplary non-transient memory includes random access memory, read onlymemory, flash memory or the like. Such non-transient memory can beelectrically based or optically based. Further, the messages describedherein may be generated by the components and result in various physicaltransformations.

Finally, as used herein any reference to “one embodiment” or “anembodiment” or “implementation: means that a particular element,feature, structure, or characteristic described in connection with theembodiment or implementation is included in at least one embodiment orimplementation. The appearances of the phrase “in one embodiment” or “inone implementation” in various places in the specification are notnecessarily all referring to the same embodiment or implementation.

In accordance with the present disclosure, messages or data transmittedbetween nodes may be processed by circuitry within the inputinterface(s), and/or the output interface(s) and/or the control module.Circuitry could be analog and/or digital, components, or one or moresuitably programmed microprocessors and associated hardware andsoftware, or hardwired logic. Also, certain portions of theimplementations have been described as “components” that perform one ormore functions. The term “component,” may include hardware, such as aprocessor, an application specific integrated circuit (ASIC), or a fieldprogrammable gate array (FPGA), or a combination of hardware andsoftware. Software includes one or more computer executable instructionsthat when executed by one or more component cause the component toperform a specified function. It should be understood that thealgorithms described herein are stored on one or more non-transientmemory. Exemplary non-transient memory includes random access memory,read only memory, flash memory or the like. Such non-transient memorycan be electrically based or optically based. Further, the messagesdescribed herein may be generated by the components and result invarious physical transformations.

Consistent with an aspect of the present disclosure, electrical signalsor digital subcarriers are generated in a Digital Signal Processor basedon independent input data streams. Drive signals are generated based onthe digital subcarriers, and such drive signals are applied to anoptical modulator, including, for example, a Mach-Zehnder modulator. Theoptical modulator modulates light output from a laser based on the drivesignals to supply optical subcarriers, each of which corresponding to arespective digital subcarrier. Each of the optical subcarriers may berouted separately through a network and received by optical receiversprovided at different locations in an optical communications network,where at least one of the optical subcarriers may be processed, and theinput data stream associated with such optical subcarrier(s) is output.

Accordingly, instead of providing multiple transmitters, each beingassociated with a respective optical signal, one transmitter, having, inone example, a laser, may be provided that supplies multiplesubcarriers, one or more of which carries data that may be independentlyroutable to a corresponding receiver provided at a unique location.Thus, since fewer transmitters are required consistent with the presentdisclosure, system costs may be reduced.

Since the subcarriers may be transmitted over different transmissionpaths to receivers having different capacities or other properties,characteristics of each subcarriers may be tuned or adjusted to provideoptimal performance. For example, the modulation format, data rate,and/or baud rate may be selected for a given subcarrier based on aparticular path through the network and capacity or bandwidth of theintended receiver. These parameters may be selected to be different forother subcarriers that are transmitted over different paths to differentreceivers in the network. In one example, the modulation format may beselected from binary phase shift keying (BPSK), quadrature phase shiftkeying (QPSK), and m-quadrature amplitude modulation (m-QAM, where m isan integer).

Consistent with a further aspect of the present disclosure, efficientclock or phase recovery of a received signals may be made more efficientby sensing data or information associated with one subcarrier having aspectral width that is wider than other subcarriers associated with aparticular carrier.

FIG. 1 is a diagram of a simplified view of an optical network 200 inwhich systems and/or methods described herein may be implemented. In oneexample, optical network 200 may constitute part of a larger networkincluding multiple nodes arranged as a mesh or a ring, as discussed ingreater detail below. As illustrated in FIG. 1, the optical network 200may include a transmitter (Tx) module 210, and/or a receiver (Rx) module220. In some implementations, the transmitter module 210 may beoptically connected to the receiver module 220 via one or more link 230.Additionally, the link 230 may include one or more optical amplifiers240 that amplify an optical signal as the optical signal is transmittedover the link 230.

The transmitter module 210 may include a number of optical transmitters212-1 through 212-M (where M is greater than or equal to one),waveguides 214, and/or optical multiplexers 216. In someimplementations, the transmitter module 210 may include additionalcomponents, fewer components, different components, or differentlyarranged components.

Each optical transmitter 212 may receive data for one or more datainputs 352, each of which may include a plurality of client data streams352-1 to 352-4 discussed in greater detail below with reference to FIG.2. Based on a respective data input, each transmitter provides a carrierand an associated plurality of subcarriers. The carrier has a wavelengthequal to or substantially equal to the wavelength of continuous wave(CW) light output from a laser (see FIG. 2) and each subcarrier may havea frequency or wavelength that is different than the carrier wavelengthThe transmitter 212 is described in greater detail below in relation toFIG. 2.

Remaining now with FIG. 1, in one implementation, the transmitter module210 may include 5, 10, or some other quantity of the opticaltransmitters 212. In one example, the carrier wavelength of the opticalsignals supplied by each transmitter 212 may be tuned to conform to awavelength grid, such as a standard grid published by theTelecommunication Standardization Sector (ITU-T). The carrierwavelengths may also be tuned to conform to a flexible grid in which thespacing between the carrier wavelengths is non-uniform. Moreover, thecarrier wavelengths may be tuned to be more tightly packed spectrally tocreate a super channel.

The waveguides 214 may include an optical link or some other link totransmit output optical signals (each including a carrier and aplurality of subcarriers) of the optical transmitters 212. In someimplementations, each optical transmitter 212 may include one waveguide214, or multiple waveguides 214, to transmit output optical signals ofthe optical transmitters 212 to the optical multiplexer 216.

The optical multiplexer 216 may include a power combiner, an arrayedwaveguide grating (AWG) or some other multiplexer device. In someimplementations, the optical multiplexer 216 may combine multiple outputoptical signals, associated with the optical transmitters 212, into asingle optical signal (e.g., a WDM signal). In some implementations, theoptical multiplexer 216 may combine multiple output optical signals,associated with the optical transmitters 212, in such a way as tocombine polarization multiplexed signals (e.g., also referred to hereinas a WDM signal). A corresponding waveguide may output the WDM signal onan optical fiber, such as the link 230. The optical multiplexer 216 mayinclude waveguides connected to an input and/or an output.

As further shown in FIG. 1, the optical multiplexer 216 may receiveoutput optical signals outputted by the optical transmitters 212, andoutput one or more WDM signals. Each WDM signal may include one or moreoptical signals, such that each optical signal includes one or morewavelengths. In some implementations, each optical signal in the WDMsignal may have a first polarization (e.g., a transverse magnetic (TM)polarization), and a second, substantially orthogonal polarization(e.g., a transverse electric (TE) polarization). Alternatively, eachoptical signal may have one polarization.

The link 230 may comprise an optical fiber. The link 230 may transportone or more optical signals. The amplifier 240 may include one or moreamplification device, such as a doped fiber amplifier and/or a Ramanamplifier. The amplifier 240 may amplify the optical signals as theoptical signals are transmitted via the link 230.

In addition, one or more OADMs 229 may be provided along the fiber link230. The OADMs 229 may be configured to add or drop one or more opticalsubcarriers included in the optical signals output from eachtransmitters. For example, as further shown in FIG. 1, subcarrier SC1 ofa first optical signal may be added and/or dropped (as indicated by thearrows shown in FIG. 1) at OADM 229-1, and subcarrier SC2 of anotheroptical signal may be added and/or dropped (as shown by the arrows inFIG. 1) at OADM 229-2.

The receiver module 220 may include optical demultiplexer 222,waveguides 224, and/or optical receivers 226-1 through 226-N (where N isgreater than or equal to one). In some implementations, the receivermodule 220 may include additional components, fewer components,different components, or differently arranged components.

The optical demultiplexer 222 may include an AWG, a power splitter, orsome other demultiplexer device. The optical demultiplexer 222 maysupply multiple optical signals based on receiving one or more opticalsignals, such as WDM signals, or components associated with the one ormore optical signals. Additionally, the optical demultiplexer 222 mayinclude waveguides 224.

The waveguides 224 may include an optical link or some other link totransmit optical signals, output from the optical demultiplexer 222, tothe optical receivers 226. In some implementations, each opticalreceiver 226 may receive optical signals via a single waveguide 224 orvia multiple waveguides 224.

As discussed in greater detail below, the optical receivers 226 may eachinclude one or more photodetectors and related devices to receiverespective input optical signals outputted by the optical demultiplexer222, detect the subcarriers associated with the input optical signals,convert the subcarriers to voltage signals, convert the voltage signalsto digital samples, and process the digital samples to produce outputdata corresponding to the one or more data streams, such as the inputclient data streams 352-1 to 352-4 associated with input data 352provided to transmitter 212-1, for example. In some implementations,each of the optical receivers 226 may include a local oscillator, ahybrid mixer, a detector, an ADC, an RX DSP, and/or some othercomponents, as described in greater detail below in relation to FIG. 6.

While FIG. 1 shows the optical network 200 as including a particularquantity and arrangement of components, in some implementations, theoptical network 200 may include additional components, fewer components,different components, or differently arranged components. Also, in someinstances, one of the devices illustrated in FIG. 1 may perform afunction described herein as being performed by another one of thedevices illustrated in FIG. 1.

FIG. 2 is a diagram illustrating an example of components of the opticaltransmitter 212 in greater detail. As shown in FIG. 2, the opticaltransmitter 212 may include a TX DSP 310, two digital-to-analogconverters (DACs) 320-1 and 320-2 (referred to generally as DACs 320 andindividually as DAC 320), a laser 330, modulators 340-1 and 340-2(referred to generally as modulators 340 and individually as modulator340), and a splitter 350.

In some implementations, the TX DSP 310 and the DAC 320 may beimplemented using an application specific integrated circuit (ASIC)and/or may be implemented on a single integrated circuit, such as asingle PIC. In some implementations, the laser 330 and the modulator 340may be implemented on a single integrated circuit, such as a singlephotonic integrated circuit (PIC). In some other implementations, the TXDSP 310, the DAC 320, the laser 330, and/or the modulator 340 may beimplemented on one or more integrated circuits, such as one or morePICS. For example, in some example implementations, components ofmultiple optical transmitters 212 may be implemented on a singleintegrated circuit, such as a single PIC, to form a super-channeltransmitter.

The TX DSP 310 may comprise a digital signal processor. The TX DSP 310may receive input data from multiple data sources, each of whichsupplying a respective one of the plurality of Client Data Streams 352-1through 352-4. In general, “N” number of Client Data Streams 3521 to352-N can be used. For explanatory purposes, four Client Data Streams352 (N=4) are used in relation to FIG. 2. The TX DSP 310 may determinethe signal to apply to the modulator 340 to generate multiple opticalsubcarriers. Digital subcarriers may comprise electronic signalsgenerated in the TX DSP 310 that correspond to respective opticalsubcarriers.

In some implementations, the TX DSP 310 may receive streams of data(such as one or more of the Client Data Streams 352-1 to 352-4), map thestreams of data into each of the digital subcarriers, independentlyapply spectral shaping to each of the digital subcarriers, and obtain,based on the spectral shaping of each of the digital subcarriers, asequence of values to supply to the DAC 320. In some implementations,the TX DSP 310 may generate the digital subcarriers using time domainfiltering and frequency shifting by multiplication in the time domain.The TX DSP 310 will be further described in relation to FIG. 3.

The DAC 320 may comprise a digital-to-analog converter. The DAC 320 mayreceive the sequence of values and, based on the sequence of values,generate the analog or voltage signals to apply to the modulator 340.

The laser 330 may include a semiconductor laser, such as a distributedfeedback (DFB) laser, or some other type of laser. The laser 330 mayprovide an output optical light beam to the modulator 340.

The modulator 340 may include a Mach-Zehnder modulator (MZM), such as anested MZM, or another type of modulator. The modulator 340 may receivethe optical light beam from the laser 330 and the voltage signals fromthe DAC 320, and may modulate the optical light beam, based on thevoltage signals, to generate a multiple subcarrier output signal(s),such as Output TE Signal 342-1 and Output TM Signal 342-2.

The splitter 350 may include an optical splitter that receives theoptical light beam from the laser 330 and splits the optical light beaminto two branches: one for the first polarization and one for the secondpolarization. In some implementations, the two optical light beams mayhave approximately equal power. The splitter 350 may output one opticallight beam to modulator 340 including first and second modulators 340-1and 340-2, each of which may include a Mach-Zehnder modulator.

The modulator 340-1 may be used to modulate signals of the firstpolarization. The modulator 340-2 may be used to modulate signals of thesecond polarization.

In some implementations, one or more subcarrier may be modulated by themodulator 340 to carry data at different rates (see FIG. 4A illustratingexemplary subcarriers). For example, a first subcarrier SC1 may carrydata at a first rate and subcarrier SC2 may carry data at a differentrate that is higher or lower than the first rate. In addition, one ormore subcarrier may be modulated by the modulator 340 to carry data withdifferent baud rates (see FIG. 4A illustrating exemplary subcarriers).For example, the first subcarrier SC1 may carry data at or have anassociated a first baud rate and the second subcarrier SC2 may carrydata at or have an associated second baud rate that is higher or lower(different) than the first baud rate.

In some implementations, a first one of a plurality of subcarriers SC1may be modulated in accordance with a first modulation format and asecond one of the plurality of subcarriers SC2 may be modulated inaccordance with a second modulation format different than the firstmodulation format (see FIG. 4A illustrating exemplary subcarriers). Inone implementation, the first modulation format may be one of BPSK,QPSK, and m-QAM, where m is an integer, and the second modulation formatmay be another one of BPSK, QPSK, and m-QAM. In one implementation, thefirst modulation format may be one of BPSK, QPSK, and m-QAM, where m isan integer, and the second modulation format may be an intensitymodulation format.

In some implementations, a plurality of the subcarriers may have avariety of combinations of modulation and data rates configured by thetransmitter and/or by a plurality of transmitters 212. The particularcombination of modulation and data rates of the subcarriers may beconfigured based on the desired distance of transmission, desired errorrate, desired data rate, and/or other requirements and/or restrictionsfor the optical network 200 and/or the end client.

In some implementations, two DACs 320 may be associated with eachpolarization. In these implementations, two DACs 320-1 may supplyvoltage signals to the modulator 340-1, and two DACs 320-2 may supplyvoltage signals to the modulator 340-2. In some implementations, theoutputs of the modulators 340 may be combined back together usingcombiners (e.g., optical multiplexer 216) and polarization multiplexing.

While FIG. 2 shows the optical transmitter 212 as including a particularquantity and arrangement of components, in some implementations, theoptical transmitter 212 may include additional components, fewercomponents, different components, or differently arranged components.The quantity of DACs 320, lasers 330, and/or modulators 340 may beselected to implement an optical transmitter 212 that is capable ofgenerating polarization diverse signals for transmission on an opticalfiber, such as the link 230. In some instances, one of the componentsillustrated in FIG. 2 may perform a function described herein as beingperformed by another one of the components illustrated in FIG. 2.

FIG. 3 shows an example of the digital signal processor (TX DSP) 310 ofthe transmitter 212 in greater detail. In this example, four of theClient Data Streams 352 are shown. The digital signal processor 310 mayinclude FEC encoders 405-1 to 405-4 (referred to generally as FECencoders 405 and individually as FEC encoder 405), input bits components420-1 to 420-4 (referred to generally as input bits components 420 andindividually as input bits component 420), four bits-to-symbolcomponents 430-1 to 430-4 (referred to generally as bits-to-symbolcomponents 430 and individually as bits-to-symbol component 430), fouroverlap-and-save buffers 256 440-1 to 440-4 (referred to generally asoverlap-and-save buffers 440 and individually as overlap-and-save buffer440), four fast Fourier transform functions (FFT) 256 components 450-1to 450-4 (referred to generally as FFT components 450 and individuallyas FFT component 450), four replicator components 460-1 (referred togenerally as replicator components 460 and individually as replicatorcomponent 460), four pulse shape filters 470 (referred to generally aspulse shape filters 470 and individually as pulse shape filter 470), aninverse FFT (IFFT) 2048 component 490, and a take last 1024 component495. Optionally, the TX DSP 310 may further comprise one or morezero-bit-insertion-block circuitry components 475 (referred to generallyas zero-bit-insertion-block circuitry components 475 and individually aszero-bit-insertion-block circuitry component 475), and a memory 2048array 480. Optionally, the TX DSP 310 may further comprise fourzero-bit-insertion-block circuitry components 475 (referred to generallyas zero-bit-insertion-block circuitry components 475 and individually aszero-bit-insertion-block circuitry component 475), and a memory 2048array 480.

For each of the Client Data Streams 352, the digital signal processor(TX DSP) 310 of the transmitter 301 may contain one each of the FECencoders 405, the input bits components 420, the bits-to-symbolcomponents 430, the overlap-and-save buffers 440, the fast Fouriertransform functions (FFT) components 450, the replicator components 460,the pulse shape filters 470, and the zero-bit-insertion-block circuitrycomponents 475.

Each of the FEC encoders 405-1 to 405-4 may receive a particular one ofthe plurality of independent input data streams of bits (illustrated asexemplary Client Data Streams 352-1 to 352-4) from a respective one of aplurality of data sources and perform error correction coding on acorresponding one of the input Client Data Streams 352, such as throughthe addition of parity bits. The FEC encoders 405-1 to 405-4 may bedesigned to generate timing skew between the subcarriers to correct forskew induced by link(s) between the transmitter module 210 and thereceiver module 220 in the optical network 200.

Input bits component 420 may process, for example, 128*X bits at a time,where X is an integer. For dual-polarization Quadrature Phase ShiftKeying (QPSK), X is four. For higher modulation formats, X may be morethan four. For example, for an 8-quadrature amplitude modulation (QAM)format, X may be eight and for a 16 QAM modulation format, X may besixteen. Accordingly, for such 8 QAM modulation, eight FEC encoders 405may be provided, each of which may encode a respective one of eightindependent input data streams (e.g., eight of the Client Data Streams352) for a corresponding one of eight digital subcarriers correspondingto eight optical subcarriers. Likewise, for 16 QAM modulation, sixteenFEC encoders 405 may be provided, each of which may encode a respectiveone of sixteen independent input data streams (e.g., sixteen of theClient Data Streams 352) for a corresponding one of sixteen subcarrierscorresponding to sixteen optical subcarriers.

The bits-to-symbol component 430 may map the bits to symbols on thecomplex plane. For example, the bits-to-symbol components 430 may mapfour bits or other numbers of bits to a symbol in the dual-polarizationQPSK constellation or other modulation format constellation.Accordingly, each of the components or circuits 430 may define ordetermine the modulation format for a corresponding subcarrier. Inaddition, components or circuits 405, 420, and 430 may define ordetermine the baud rate and or data rate for each subcarrier. Therefore,the modulation format, baud rate and data rate may be selected for eachsubcarrier by these circuits. For example, control inputs may beprovided to these circuits so that the desired modulation format, baudrate and data rate may be selected.

The overlap-and-save buffer 440 may buffer 256 symbols, in one example.The overlap-and-save buffer 440 may receive 128 symbols at a time fromthe bits-to-symbol component 430. Thus, the overlap-and-save buffer 440may combine 128 new symbols, from the bits-to-symbol component 430, withthe previous 128 symbols received from the bits-to-symbol component 430.

The FFT component 450 may receive 256 symbols from the overlap-and-savebuffer 440 and convert the symbols to the frequency domain using, forexample, a fast Fourier transform (FFT). The FFT component 450 may form256 frequency bins, for example, as a result of performing the FFT.Components 440 and 450 may carry out the FFT for each subcarrier basedon one sample per symbol (per baud) to thereby convert time domain ordata symbols received by FFT component 550 into frequency domain datafor further spectral shaping (requiring more than one sample/baud orsymbol) by filters 470.

The replicator component 460 may replicate the 256 frequency bins, inthis example, or registers to form 512 frequency bins (e.g., for T/2based filtering of the subcarrier). This replication may increase thesample rate.

The pulse shape filter 470 may apply a pulse shaping filter to the datastored in the 512 frequency bins to thereby provide the digitalsubcarriers with desired spectral shapes and such filtered subcarriersare multiplexed and subject to the inverse FFT 490, as described below.The pulse shape filter 470 may calculate the transitions between thesymbols and the desired spectrum so that the subcarriers can be packedtogether on the channel. The pulse shape filter 470 may also be used tointroduce timing skew between the subcarriers to correct for timing skewinduced by links between nodes in the optical network 200. The pulseshape filters 470 may be raised cosine filters.

The pulse shape filter 470 may have a variable bandwidth. In someimplementations, the bandwidth of the subcarriers may be determined bythe width of the pulse shape filters 470. The pulse shape filters 470may manipulate the digital signals of the subcarriers or digitalsubcarriers to provide such digital subcarriers with an associatedspectral width. In addition, as generally understood, the pulse shapefilter 470 may have an associated “roll-off” factor (a). Consistent withthe present disclosure, however, such “roll-off” may be adjustable orchanged in response to different control inputs to the pulse shapefilter 470. Such variable roll-off results in the pulse shape filter 470having a variable or tunable bandwidth, such that each subcarrier mayhave a different spectral width. In a further example, one of thesubcarriers may have an associated spectral width that is wider than theremaining subcarriers. It is understood that the control inputs may beany appropriate signal, information, or data that is supplied to thepulse shape filter 470, such that the “roll-off” is changed in responseto such signal, information, or data.

The four zero-bit-insertion-block circuitry components 475 may comprisecircuitry to receive the four digital subcarriers from the four pulseshape filters 470 and may output zeros or other bits in bits between ablock of data bits of a first subcarrier and a block of data bits of asecond subcarrier to the memory array 480 in order to adjust thefrequency spacing or gap between the optical subcarriers, as discussedin greater detail below.

The memory array 480 may receive all four of the subcarriers from thezero-bit-insertion-block circuitry components 475 and the zeros from thefour zero-bit-insertion-block circuitry components 475. The memory array480 may store the outputs of the subcarriers and output an array of thefour subcarriers and the zeros from the four zero-bit-insertion-blockcircuitry components 475 to the IFFT component 490.

The IFFT component 490 may receive the 2048 element vector and returnthe signal back to the time domain, which may now be at 64 GSample/s.The IFFT component 490 may convert the signal to the time domain using,for example, an inverse fast Fourier transform (IFFT).

The take last 1024 component 495 may select the last 1024 samples, forexample, from IFFT component 490 and output the 1024 samples to the DACs320 of the transmitter 212 (such as at 64 GSample/s, for example).

While FIG. 3 shows the TX DSP 310 as including a particular quantity andarrangement of functional components, in some implementations, the TXDSP 310 may include additional functional components, fewer functionalcomponents, different functional components, or differently arrangedfunctional components.

Returning now to FIG. 2, as previously described, the DACs 320 mayconvert the received samples from the take last component 495 of the TXDSP 310. The modulator 340 may receive the optical light beam from thelaser 330 and the voltage signals from the DAC 320, and may modulate theoptical light beam or CW light from laser 330, based on the voltagesignals, to generate a multiple subcarrier output signal, such as OutputTE Signal 342-1 and Output TM Signal 342-2.

FIGS. 4A-4E illustrate examples of subcarriers SC1 to SC4 that may beoutput from the transmitter 212 (similar subcarriers may be output fromtransmitters in transceivers located at other nodes). In one example,the subcarriers SC1 to SC4 may not spectrally overlap with one anotherand may be, for example, Nyquist subcarriers, which may have a frequencyspacing equal to or slightly larger than the individual subcarrierbaud-rate.

As illustrated in FIG. 4A, the subcarriers may have one or more spectraor bandwidths, such as, for example, S3 (subcarrier SC3) and S4(subcarrier SC4) above frequency f0, which may correspond to a centerfrequency (f0) of the laser 330 of the transmitter 212. In addition, thesubcarriers may have one or more spectra or bandwidths, such as for S1(subcarrier SC1) and S2 (subcarrier SC2) below frequency f0.

In one example, the number of subcarriers equals a number of theindependent input Client Data Streams 352. For example, Client DataStreams 352-1 to 352-4 from FIG. 3 may be four independent input datastreams corresponding to four subcarriers SC1 to SC4 in FIG. 4A, suchthat each of the subcarriers carries data or information associated witha respective one of the Client Data Streams. In one example, the numberof subcarriers is more than the number of the independent input ClientData Streams 352. For example, Client Data Streams 352-1 to 352-3 fromFIG. 3 may be three independent input data streams mapped to foursubcarriers SC1 to SC4. Two or more of the subcarriers, such as thesubcarriers SC3 and SC4, may carry one of the Client Data Streams 352-3.Such an arrangement allows for more data capacity to be dedicated to aparticular Client Data Stream 352.

Frequency bandwidth and roll-off of the subcarriers may be determined byappropriate input to the pulse shape filters 470. The laser frequency(f0) may be centrally positioned within the frequency (f) of thefilters' bandwidth. As illustrated in FIG. 4A, the filter bandwidths foreach of the four pulse shape filters 470 may be the same, for example,and may all have the same roll-off factor (for example, α=0.3),producing four subcarriers SC1-SC4 each having the same bandwidth. Asillustrated in FIG. 4B, the filter bandwidths for each of the four pulseshape filters 470 may be the same, for example, and may all have thesame roll-off factor (for example, α=0.7) differing from the roll-offfactor of the example of FIG. 4A, producing four subcarriers SC1-SC4each having the same bandwidth, but with a larger bandwidth thansubcarriers produced by a pulse shape filter 470 having a smallerroll-off factor. Thus, the roll-off factor for each of filters 470 maybe controlled or adjusted so that corresponding optical subcarriers havedifferent spectral widths, as noted above.

FIG. 4C illustrates another example in which the bandwidth of the foursubcarriers is the same. In the example of FIG. 4C, the baud rate ofeach subcarrier is 8.039, and the shaping factor is 1/16 (6.25%), makingthe total width of each subcarrier 8.039*(1+ 1/16)=8.54 GHz. In someimplementations, the roll-off factor can be assigned to be very narrowfor the majority of the subcarriers, while one subcarrier is given awider roll-off factor. This allows for channel spacing to be tighterthan would be possible with conventional shaping and clock recovery.That is, since the majority of subcarriers in this example, have anarrow bandwidth, more subcarriers can be accommodated within a givenamount of spectrum, and, therefore, provide greater data carryingcapacity for a given link. Clock and/or phase recovery based on thewider subcarrier is discussed in greater detail below.

As illustrated in FIGS. 4D and 4E, in some implementations, the filterbandwidths for one or more of the four pulse shape filters 470 may bedifferent that the filter bandwidths of one or more of the other pulseshape filters 470, thereby resulting in one or more of the subcarriershaving a different bandwidth than one or more of the other subcarriers.Additionally or alternately, one or more of the four pulse shape filters470 may have a different roll-off factor (α) than one or more of theother pulse shape filters 470, thereby resulting in one or moresubcarriers having a different bandwidth than the other subcarriers. Forexample, a first, third, and fourth of the pulse shape filters 470-1,470-3, 470-4 may have a first roll-off factor (such as α=0.3) while asecond of the pulse shape filters 470-2 may have a roll-off factordifferent than the other three (such as α=0.7), such that the first,third, and fourth subcarriers SC1, SC3, and SC4, have a first bandwidthand the second subcarrier SC2 has a second bandwidth different than thebandwidths of the other subcarriers. In some implementations, thesubcarrier with the larger bandwidth than the other subcarriers may beused to carry clock-recovery information for a plurality of thesubcarriers, as will be described in relation to FIG. 7.

In the example shown in FIG. 4E, the first subcarrier SC1 is shaped with1.5% roll-off factor, for example; the second subcarrier SC2 is shapedwith 6.25% roll-off factor, for example; and the third subcarrier SC3and the fourth subcarrier SC4 are shaped with 1.5% roll-off factor, forexample. A 1.5% roll-off factor on 8.039 GBaud maps to 8.16 GHz. In thisexample, total spectral width is reduced by 800 MHz in comparison to theexample illustrated in FIG. 4D.

Referring now to FIG. 3 and FIGS. 5A-5D, in some implementations, thesubcarriers may have gaps, or spacing, between the subcarriers createdby the zero-bit-insertion-block circuitry components 475. Thezero-bit-insertion-block circuitry components 475 may insert zeros orother bits within certain locations between the data from a firstsubcarrier and the data associated with one or more second subcarriersinto the memory array 480, which may result in one or more frequencygaps between the optical subcarriers of varying or constant width, asdescribed below.

Varying or controlling the frequency gap will next be described ingreater detail with reference to FIG. 5A, which illustrates memorylocations 0 . . . 2048 included in memory array 480. The memory array480 may include, in one example, an array of such memory locations,whereby selected locations store complex numbers output from filters470, as well as, in one example, 0 bits. Such complex numbers constitutefiltered frequency domain data associated with each subcarrier. Thesenumbers may then be output to IFFT component 490, which, in turnsupplies a time domain signal, and based, on such time domain signal,analog signals are generated for driving modulators 340 to output theoptical subcarriers. Thus, by selecting memory locations that store 0bits and other locations that store the frequency domain data, theinputs to IFFT component 490 may be set to result in particularfrequency assignments and spacings of the optical subcarriers.

In the example shown in FIG. 5A, filters 470-1 to 470-4 output frequencydomain data to location groupings L1 to L4, respectively in memory 480.Each of memory location groupings L-1 to L-4 may store such frequencydomain data as complex numbers, and each such complex number may bestored in a respective location in each grouping. In one example, eachof memory location groupings L-1 to L-4 may have 256 locations, each ofwhich storing a respective one of 256 complex numbers. In addition,zero-bit-insertion-block circuitry components 475 may provide zero bitsor other numbers to location groupings Z1 to Z4, respectively, in memory480. Memory location groupings Z1 to Z5 including those memory remaininglocations in memory 480 other than the locations included in locationsL1 to L4. When the resulting combination of numbers in locationgroupings L1 to L4 and the zero bits stored in locations Z1 to Z5 ofmemory 480 are output to the IFFT component 490, the IFFT component 490outputs time domain signals, in digital form, that result in opticalsubcarriers SC1 to SC4 having frequencies f1 to f4, respectively, asshown in FIG. 5A, and associated frequency gaps G1-1 to G1-3, as furthershown in FIG. 5A.

As further shown in FIG. 5a , the frequency domain data stored inlocations L-1 is associated with and corresponds to data carried bysubcarrier SC3; the frequency domain data stored in locations L-2 isassociated with and corresponds to data carried by subcarrier SC4; thefrequency domain data stored in locations L-3 is associated with andcorresponds to data carried by subcarrier SC1; and the frequency domaindata stored in locations L-1 is associated with and corresponds to datacarried by subcarrier SC4.

Similarly, as shown in FIG. 5B, the filters 570-1 to 570-4 outputfrequency domain data to location groupings L2-1 to L2-4, respectivelyin the memory 480. In addition, zero-bit-insertion-block circuitrycomponents 475 may provide zero bits to location groupings Z2-1 to Z2-4,respectively, in the memory 480. When the resulting combination ofnumbers stored in location groupings L1 to L4 and the zero bits storedin locations Z1 to Z5 of memory 480 are output to the IFFT component490, the IFFT component 490 outputs time domain signals, in digitalform, that result in optical subcarriers SC1 to SC4 having frequenciesf1′ to f4′, respectively in FIG. 5B, and associated frequency gaps G2-1to G2-3, as further shown in FIG. 5B. Frequencies f1′ to f4′ may differfrom frequencies f1 to f4, and frequency gaps G2-1 to G2-3 may differfrom frequency gaps G1 to G3. Thus, based on the locations frequencydomain data and the zero bit data the gaps and frequencies of thesubcarriers can be controlled or adjusted, such that different locationsin which the frequency domain and zero bit data are stored can result indifferent subcarrier frequencies and gaps.

FIGS. 5C and 5D illustrate further examples of subcarriers havingvariable spacing between the subcarriers and varying combinations ofspacing between groups of subcarriers. For example, in FIG. 5C, a firstgroup of subcarriers SC1-SC4 in a first carrier C1 (such as from a firsttransmitter 212) are routed together, with a gap G2 between the firstcarrier C1 and a second carrier C2 (such as from a second transmitter212) having a second group of subcarriers SC1-SC4. Additionally, FIG. 5Cillustrates another pattern of carriers Cn−1, Cn, Cn+1, in which a pairof subcarriers SC2, SC4 from a first carrier Cn−1 are routed with a pairof subcarriers SC3, SC1 from a second subcarrier Cn; while a pair ofsubcarriers SC2, SC4 from the second carrier Cn are routed with a pairof subcarriers SC3, SC1 from a third subcarrier Cn+1; with a gap G2between the first subcarrier SC1 in Cn−1 and the second subcarrier SC2in Cn−1, and also with a gap G2 between the first subcarrier SC1 in Cnand the second subcarrier SC2 in Cn, and so on. The pattern of groupingof and spacing between subcarriers may repeat for multiple carriers Cn,or may vary. Each of carriers Cn may be supplied from a correspondingone of transmitters 370.

In another example, FIG. 5D illustrates a variety of combinations ofrouting of subcarriers with and without gaps between exemplary carriersC1, C2, C3, and C4 and/or subcarriers within the carriers Cn. In thisexample, an Intra-Carrier Gap (G) may be allocated between 0, 1, 2 or Nof the subcarriers. The Intra-Carrier Gap (G) may be the total gapbudgeted for the channel. The size of the gaps G1, G2, . . . Gn, betweenthe subcarriers may range from zero GHz to a maximum of the totalIntra-Carrier Gap G. In the example illustrated in FIG. 5D, G1=6.25 GHz.The frequency width of the subcarriers SC1, SC2, SC3, SC4 in a carrierCn may vary. In the example of FIG. 5D, a combination of gaps G1 is usedwith the illustrated carriers C1-C4. For example, in carrier C1, a gapG1 is shown between each of the subcarriers SC1-SC4, and between thecarrier C1 and the carrier C2. Further in this example, in carriers C2and C3, no gap is shown between the respective subcarriers SC3 and SC1or SC2 and SC4, while a gap G1 is shown between the respectivesubcarriers SC1 and SC2 and between the carrier C2 and the carrier C3.In the example, carrier 4 does not have gaps between the subcarriers orbetween carrier 4 and carrier 3, but does have a gap between carrier 4and any additional carriers.

In one implementation, the subcarriers may not occupy the centerfrequency ω_c (that is, the laser wavelength). The frequency width of acarrier (Cn) may equal the sum of the frequency width of the subcarriersplus the sum of the frequency width of the gaps Gn (that is, the totalIntra-Carrier Gap G). In another implementation, up to a maximum of halfof the total Intra-Carrier gaps G may be allocated on either side of thecenter frequency ω_c, that is, the laser frequency. It will beunderstood that these combinations of spacing are exemplary, and thatany combination of spacing between subcarriers and/or carriers may beused.

The variable spacing of the subcarriers may be based at least in part onthe routing and/or destination of the subcarriers. For example, thetypes of filters in the OADMs 229 and/or their widths and/or the numberof filters in the route through the optical network 200 that thesubcarrier will take, as well as the number and locations of receivers226, and the capacity of such receivers 226, may determine the number ofsubcarriers, the width of the subcarriers, the frequencies of thesubcarriers, and/or the spacing between the subcarriers that aretransmitted in a particular optical network 200. The spacing of thesubcarriers may be based at least in part on one or more data rate ofone or more of the subcarriers.

An example of subcarrier frequency selection based on filter bandwidthwill next be described with reference to FIG. 5e . As noted above,optical signals including subcarriers may be output from transmitters212 onto optical fiber link 230. The optical signals may be transmittedthrough OADMs 229-1 and 229-2 coupled along fiber link 230. Each ofOADMs 229-1 and 229-2 may include wavelength selective switches, each ofwhich may further including one or more optical filters. One of theseoptical filters provided in OADM 229-1, for example, may have abandwidth or transmission characteristic 529-1 defined by edgefrequencies f2 and f4, and at least one of the optical filters in OADM229-2 may have a bandwidth or transmission characteristic 529-2 definedby frequencies f5 and f6. In order to transmit a subcarrier, such assubcarrier SC1 through filters in both OADM 229-1 and 229-2, thefrequency of the subcarrier is preferably selected to be within a hightransmission frequency range R that is common to both filter bandwidths529-1 and 529-2. As further shown in FIG. 5E, range R is defined by edgefrequency F4 of bandwidth 529-1 and edge frequency f5 of bandwidth529-2. Accordingly, the frequency f1 of subcarrier SC1 is controlled orselected by controlling the subcarrier gap in a manner similar to thatdescribed above so that SC1 falls within the high transmission frequencyrange R that is common to or overlaps between filter bandwidths 529-1and 529-2.

Returning now to FIG. 1, in one example, subcarriers that are outputfrom the transmitter 212 may be supplied to the multiplexer 216 and sentvia the link 230 to one or more receiver module, such as receiver module220, which may select data carried by one of such subcarriers, asdescribed in greater detail below with reference to FIGS. 6 and 7.

At the receiver module 220, the subcarriers may be supplied to one ormore of the receivers 226. FIG. 6 illustrates an exemplary one of theoptical receivers 226 of the receiver module 220. The optical receiver226 may include a polarization splitter 605 (having a first output 606-1and a second output 606-2), a local oscillator laser 610, twoninety-degree optical hybrids or mixers 620-1 and 620-2 (referred togenerally as hybrid mixers 620 and individually as hybrid mixer 620),two detectors 630-1 and 630-2 (referred to generally as detectors 630and individually as detector 630, each including either a singlephotodiode or balanced photodiode), two analog-to-digital converters(ADCs) 640-1 and 640-2 (referred to generally as ADCs 640 andindividually as ADC 640), and a receiver digital signal processor (RXDSP) 650.

The polarization beam splitter (PBS) 605 may include a polarizationsplitter that splits an input optical signal 607, having subcarriers, asnoted above, into two orthogonal polarizations, such as the firstpolarization and the second polarization. The hybrid mixers 620 maycombine the polarization signals with light from the local oscillatorlaser 610. For example, the hybrid mixer 620-1 may combine a firstpolarization signal (e.g., the component of the incoming optical signalhaving a first or TE polarization output from the first output 606-1)with the optical signal from the local oscillator 610, and the hybridmixer 620-2 may combine a second polarization signal (e.g., thecomponent of the incoming optical signal having a second or TMpolarization output from the second output 606-2) with the opticalsignal from the local oscillator 610. In one example, a polarizationrotator may be provided at the second output 606-2 to rotate the secondpolarization to be the first polarization.

The detectors 630 may detect mixing products output from the opticalhybrid mixers 620, to form corresponding voltage signals. The ADCs 640may convert the voltage signals to digital samples. For example, twodetectors 630-1 (or photodiodes) may detect the first polarizationsignals to form the corresponding voltage signals, and a correspondingtwo ADCs 640-1 may convert the voltage signals to digital samples forthe first polarization signals after amplification, gain control and ACcoupling. Similarly, two detectors 630-2 may detect the secondpolarization signals to form the corresponding voltage signals, and acorresponding two ADCs 640-2 may convert the voltage signals to digitalsamples for the second polarization signals after amplification, gaincontrol, and AC coupling.

The RX DSP 650 may process the digital samples for the first and secondpolarization signals to generate resultant data, which may be outputtedas output data 652, such as Client Data Streams 352.

While FIG. 6 shows the optical receiver 226 as including a particularquantity and arrangement of components, in some implementations, theoptical receiver 226 may include additional components, fewercomponents, different components, or differently arranged components.The quantity of detectors 630 and/or ADCs 640 may be selected toimplement an optical receiver 226 that is capable of receiving apolarization diverse signal. In some instances, one of the componentsillustrated in FIG. 6 may perform a function described herein as beingperformed by another one of the components illustrated in FIG. 6.

Consistent with the present disclosure, in order to select one or moresubcarriers at a remote node, the local oscillator laser 610 may betuned to output light having a wavelength relatively close to theselected subcarrier(s) wavelength(s) to thereby cause a beating betweenthe local oscillator light and the selected subcarrier(s). Such beatingwill either not occur or will be significantly attenuated for the othernon-selected subcarriers so that data from the Client Data Stream(s) 352carried by the selected subcarrier is detected and processed by the RxDSP 650.

In the example shown in FIG. 6, appropriate tuning of the wavelength ofthe local oscillator laser 610 enables selection of one of thesubcarriers, e.g., SC1, carrying signals or data indicative of ClientData Stream 352-1. Accordingly, subcarriers may be effectively routedthrough the optical network 200 to a desired receiver 226 in aparticular node of the optical network 200.

Accordingly, at each receiver 226, the local oscillator laser 610 may betuned to have a wavelength close to that of one of the subcarrierscarrying signals and data indicative of the desired client data from theClient Data Stream 352 to be output from the Rx DSP 650. Such tuning maybe achieved by adjusting a temperature or current flowing through localoscillator laser 610, which may include a semiconductor laser, such as adistributed feedback (DFB) laser or distributed Bragg reflector (DBR)laser (not shown). Thus, different optical components in each receiverare not required to select optical signals carrying a desired datastream. Rather, as noted above, the same or substantially the samecircuitry may be proved in the receiver module 220 of each node, in theoptical network 200, and signal or data selection may be achieved bytuning the local oscillator laser 610 to the desired beating wavelength.

As further shown in FIG. 6, the Rx DSP 650 may have output data 652,such that based on such output, the temperature of, or the currentsupplied to, local oscillator laser 610 may be controlled. In the caseof temperature control, a thin film heater may be provided adjacentlocal oscillator laser 610, and an appropriate current may be suppliedto such heater, based on output 652, to heat laser 610 to the desiredtemperature. Control circuitry in the Rx DSP 650 may generate output orcontrol the output signal 652. Additionally or alternatively, suchcircuitry may be provided outside the Rx DSP 650.

FIG. 7 illustrates exemplary components of an example of the receiverdigital signal processor (Rx DSP) 650 shown in FIG. 6. The RX DSP 650may include an overlap and save buffer 805, a FFT component 810, ade-mux component 815, four fixed filters 820-1 to 820-4 (referred togenerally as fixed filters 820 and individually as fixed filter 820),four polarization mode dispersion (PMD) components 825-1 to 825-4(referred to generally as PMD components 825 and individually as PMDcomponent 825), four IFFT components 830-1 to 830-4 (referred togenerally as IFFT components 830 and individually as IFFT component830), four take last 128 components 835-1 to 835-4 (referred togenerally as take last 128 components 835 and individually as take last128 component 835), four carrier recovery components 840-1 to 840-4(referred to generally as carrier recovery components 840 andindividually as carrier recovery component 840), four symbols to bitscomponents 845-1 to 845-4 (referred to generally as symbols to bitscomponents 845 and individually as symbols to bits component 845), fouroutput bits components 850-1 to 850-4 (referred to generally as outputbits components 850 and individually as output bits component 850), andfour FEC decoders 860-1 to 860-4 (referred to generally as FEC decoders860 and individually as FEC decoder 860). In one implementation, thereceiver digital signal processor 650 may optionally include a clockrecovery circuit 817.

In greater detail, the overlap and save buffer 805 may receive samplesfrom the ADCs 640-1 and 640-2. In one implementation, the ADC 640 mayoperate to output samples at 64 GSample/s. The overlap and save buffer805 may receive 1024 samples and combine the current 1024 samples withthe previous 1024 samples, received from the ADC 640, to form a vectorof 2048 elements. The FFT component 810 may receive the 2048 vectorelements, for example, from the overlap and save buffer 805 and convertthe vector elements to the frequency domain using, for example, a fastFourier transform (FFT). The FFT component 810 may convert the 2048vector elements to 2048 frequency bins as a result of performing theFFT.

The de-mux component 815 may receive the 2048 frequency bins or outputsfrom FFT component 810. The de-mux component 815 may demultiplex the2048 frequency bins to element vectors for each of the subcarriers, forexample, 512 vectors, which may have, in one example an associated baudrate of 8 Gbaud.

In some implementations, clock and/or phase recovery circuitry 817 maybe connected or coupled between the de-mux component 815 and the filter820. In cases where one of the subcarriers (such as SC2 in FIGS. 4H-4I)has a wider bandwidth, due to a corresponding roll-off in the associatedtransmitter filter 470 discussed above, than the other subcarriers, thewider subcarrier SC2 may be selected from the output of the de-muxcomponent 815 for clock recovery and the recovered or detected clock orphase related signal may be provided to the ADCs 640 in the receiver 226(see FIG. 6). The clock may be used to set and/or adjust the timing ofsampling of the ADCs 640 for the plurality of the subcarriers.

The clock may be recovered using information from all subcarriers, orfrom fewer than all the subcarriers, or just from one subcarrier. Insome implementations, clock recovery with the clock recovery circuit 817in the RX DSP 650 of the receiver 226 is based on the subcarrier withthe widest bandwidth and associated filter 470 having a correspondingroll-off (such as subcarrier SC2 in FIGS. 4D and 4E). The subcarrierwith the widest bandwidth may be used to recover the clock signal andsuch clock signal may be used for the other ADCs 640.

In one example, where the data associated with more than one ofsubcarriers SC1-SC4, such as subcarriers SC2 and SC3, is to be outputfrom the receiver 226, the clock recovered from the widest subcarrierSC2 may be used as the clock for the other subcarriers SC1, SC3, andSC4. As noted above, by reducing the frequency bandwidth of the othersubcarriers SC1, SC3, and SC4, more subcarriers fit in a given spectrumor bandwidth to thereby increase overall capacity (as shown in FIGS. 4Hand 4I). In one example, where each node outputs the data of only onesubcarrier SC1, clock recovery may be performed based on thecorresponding subcarrier SC1 to be detected at that node 202.

Fixed filters 820 may apply a filtering operation for, for example,dispersion compensation or other relatively slow varying impairment ofthe transmitted optical signals and subcarriers. The fixed filters 820may also compensate for skew across subcarriers introduced in link 230,or skew introduced intentionally in optical transmitter 212.

The PMD component 825 may apply polarization mode dispersion (PMD)equalization to compensate for PMD and polarization rotations. The PMDcomponent 825 may also receive and operate based upon feedback signalsfrom the take last 128 component 835 and/or the carrier recoverycomponent 840.

The IFFT component 830 may covert the 512 element vector, in thisexample, (after processing by the fixed filter component 820 and the PMDcomponent 825) back to the time domain as 512 samples. The IFFTcomponent 830 may convert the 512 element vector to the time domainusing, for example, an inverse fast Fourier transform (IFFT). The takelast 128 component 835 may select the last 128 samples from the IFFTcomponent 830 and output the 128 samples to the carrier recoverycomponent 840.

The carrier recovery component 840 may apply carrier recovery tocompensate for transmitter and receiver laser linewidths. In someimplementations, the carrier recovery component 840 may perform carrierrecovery to compensate for frequency and/or phase differences betweenthe transmit signal and the signal from the local oscillator 610. Aftercarrier recovery, the data may be represented as symbols in the QPSKconstellation or other modulation formats. In some implementations, theoutput of the take last 128 component 835 and/or the carrier recoverycomponent 840 could be used to update the PMD component 825.

The symbols to bits component 845 may receive the symbols output fromthe carrier recovery component 840 and map the symbols back to bits. Forexample, the symbol to bits component 845 may map one symbol, in theQPSK constellation, to X bits, where X is an integer. Fordual-polarization QPSK, X is four. In some implementations, the bitscould be decoded for error correction using, for example, FEC. Theoutput bits component 850 may output 128*X bits at a time, for example.For dual-polarization QPSK, the output bits component 850 may output 512bits at a time, for example.

The FEC decoder 860 may process the output of the output bits component850 to remove errors using forward error correction. As further shown inFIG. 7, a switch, blocking, or terminating circuit 865 may be providedto terminate one or more client data streams 352 that are not intendedfor output from receiver 226.

While FIG. 7 shows the RX DSP 650 as including a particular quantity andarrangement of functional components, in some implementations, the RXDSP 650 may include additional functional components, fewer functionalcomponents, different functional components, or differently arrangedfunctional components.

In some implementations, the subcarriers may have variable and flexiblecapacity per subcarrier, but fixed subcarrier width such as a fixed baudrate per subcarrier. Such parameters may be selected or set in a mannersimilar to that described above. An exemplary optical network 200 havingsubcarriers with flexible capacity and fixed width may includeindependent clock and carrier recovery for each subcarrier or the clockrecovery for one subcarrier may be used for other subcarriers, asdescribed previously. FIGS. 8A-8G illustrates some such examples in use.For explanatory purposes, FIGS. 8A-8G illustrate use case examples witha constant baud rate of 16 GHz per subcarrier. The subcarriers for eachexample may be transmitted from one transmitter 212 or from acombination of two or more transmitters 212.

In the example of FIG. 8A, the subcarriers SC1-SC6 are modulated at 128QAM to be transferred 100 km, with a constant baud rate of 16 GHz persubcarrier, and 175G bit rate per subcarrier. In the example of FIG. 8B,the subcarriers SC1-SC6 are modulated at 64 QAM to be transferred 500km, with a constant baud rate of 16 GHz per subcarrier, and 150G bitrate per subcarrier. In the example of FIG. 8C, the subcarriers SC1-SC6are modulated at 32 QAM to be transferred 1000 km, with a constant baudrate of 16 GHz per subcarrier, and 125G bit rate per subcarrier. In theexample of FIG. 8D, the subcarriers SC1-SC6 are modulated at 16 QAM tobe transferred 2000 km, with a constant baud rate of 16 GHz persubcarrier, and 100G bit rate per subcarrier.

In the example of FIG. 8E, the subcarriers SC1-SC4 are modulated at 128QAM to be transferred a variety of distances, with a constant baud rateof 16 GHz per subcarrier, with a variety of bit rates per subcarrier,and illustrating frequency spacing between subcarrier SC1 and subcarrierSC2, as well as between subcarrier SC3 and subcarrier SC4, such asdescribed in relation to FIGS. 5A-5D. In the example of FIG. 8F, thesubcarriers SC1-SC5 are modulated at 64 QAM to be transferred a varietyof distances, with a constant baud rate of 16 GHz per subcarrier, with avariety of bit rates per subcarrier, and illustrating frequency spacingbetween subcarrier SC3 and subcarrier SC4, such as described in relationto FIGS. 5A-5D. In the example of FIG. 8G, the subcarriers SC1-SC6 aremodulated at 16 QAM to be transferred a variety of distances, with aconstant baud rate of 16 GHz per subcarrier, and with a variety of bitrates per subcarrier.

Though the examples of FIGS. 8A-8G show particular exemplaryconfigurations of subcarriers having variable and flexible capacity persubcarrier, and having fixed subcarrier width such as a fixed baud rateper subcarrier, the subcarriers may have any combination of data rates,modulations, spacing, and/or number of subcarriers, and/or otherconfiguration factors. Additionally, two or more of the subcarriers maybe provided from one transmitter 212 or from two or more transmitters212 and from one transmitter module 210 or from two or more transmittermodules 210. The particular combination and/or configuration ofsubcarriers used may be based on requirements for transmission distance,data rates, error rates, and/or filter configurations, for example.

In some implementations, the subcarriers may have flexible width, butthe capacity of each subcarrier may be fixed. Such parameters may be setin a manner similar to that described above. To maintain a constant bitrate, the width of the subcarriers may vary as discussed above, but thedata rate may be controlled to be the same as further noted above. Anexemplary optical network 200 having subcarriers with flexible width andfixed capacity may include independent clock and carrier recovery foreach subcarrier (though the subcarriers may optionally be tiedtogether). The position of the subcarriers may be arbitrary within theanalog bandwidth, as described above. FIGS. 9A-9D illustrates some suchexamples in use. For explanatory purposes, the capacity of eachsubcarrier in FIGS. 9A-9D may be fixed at 100G per subcarrier.

In the example of FIG. 9A, the subcarriers SC1-SC6 are modulated atgreater than 64 QAM to be transferred a variety of distances with aconstant bit rate of 100G and illustrating frequency spacing betweensubcarrier SC2 and subcarrier SC3, as well as between subcarrier SC5 andsubcarrier SC6, such as described in relation to FIGS. 5A-5D. In theexample of FIG. 9B, the subcarriers SC1-SC7 are modulated atapproximately 64 QAM to be transferred a variety of distances with aconstant bit rate of 100G and illustrating frequency spacing betweensubcarrier SC5 and subcarrier SC6, such as described in relation toFIGS. 5A-5D.

In the example of FIG. 9C, the subcarriers SC1-SC4 are modulated at 32QAM to be transferred a variety of distances with a constant bit rate of100G and illustrating frequency spacing between subcarrier SC1 andsubcarrier SC2 and subcarrier SC3 and subcarrier SC4, such as describedin relation to FIGS. 5A-5D. In the example of FIG. 9D, the subcarriersSC1-SC7 are modulated at 16 QAM to be transferred a variety of distanceswith a constant bit rate of 100G.

Though the examples of FIGS. 9A-9D show particular exemplaryconfigurations of subcarriers having flexible width, but the capacity ofeach subcarrier may be fixed, the subcarriers may have any combinationof widths, modulations, spacing, and/or number of subcarriers and/orother configuration factors. Additionally, two or more of thesubcarriers may be provided from one transmitter 212 or from two or moretransmitters 212 and from one transmitter module 210 or from two or moretransmitter modules 210. The particular combination and/or configurationof subcarriers used may be based on requirements for transmissiondistance, data rates, error rates, and/or filter configurations, forexample.

FIG. 1, discussed above, shows an example of an optical network 200having a point-to-point configuration. It is understood, that othernetwork or system configurations or architectures are contemplatedherein. Examples of such architectures are discussed in greater detailbelow. The subcarriers may be transmitted and received in a variety oftypes of optical networks 200. For example, FIG. 10 illustrates anexemplary optical network 200 a having a mesh network configurationconsistent with a further aspect of the present disclosure. The meshnetwork configuration may include three or more nodes 202-1 to 202-n(referred to as nodes 202 and individually as node 202), each node 202having at least one of the transmitter module 210 and the receivermodule 220 such as previously described, but not shown in FIG. 10 forpurposes of clarity. The nodes 202 may be interconnected by one or moreof the links 230, thereby forming a mesh configuration. For purposes ofclarity, not all links 230 are numbered in FIG. 10.

In the optical network 200 a, one or more subcarriers, such assubcarriers SC1-SC4, may be routed to different nodes 202 in the opticalnetwork 200 a. For example, a first subcarrier SC1 may be routed fromnode 202-1 to node 202-2, while a second subcarrier SC2 may be routedfrom node 202-1 to node 202-8. In the optical network 200 a, one or moresubcarriers, such as subcarriers SC1-SC4, may be directed to the samenode 202. For example, four subcarriers SC1-SC4 may be routed from node202-1 to node 202-4.

In the optical network 200 a, a particular node 202 may detect multiplesubcarriers or may be configured to detect only particular subcarriersor one subcarrier. For example, node 202-4 may receive four subcarriersSC1-SC4 and detect two subcarriers SC1 and SC4.

In some implementations, a particular node 202 may receive a pluralityof subcarriers, and transfer on to another node 202 different data inone or more of the subcarriers. For example, node 202-2 may receivesubcarriers SC1 and SC3, but may place new data into subcarrier SC1-1and transmit the subcarriers SC1-1 and SC3 to node 202-3.

FIG. 11A illustrates an exemplary optical network 200 b having a ringnetwork configuration consistent with a further aspect of the presentdisclosure. The ring network configuration may include three or more ofthe nodes 202 interconnected by two or more of the links 230 to form aring. The links 230 may be bi-directional between the nodes 202. In theexample illustrated in FIG. 11A, a simple ring configuration is shownhaving five nodes 202, though it will be understood that a differentnumber of nodes 202 in a ring configuration may be included. Such aconfiguration reduces the number of optics assemblies (transmitter andreceiver) from two sets per node 202 to one set per node 202. However,one of the nodes 202 in the optical network 200 b (here, illustrated asNode 1) may still utilizing two sets of optics assemblies, such as twosets of transmitters 212 and receivers 226.

One or more subcarriers may be transmitted within the optical network200 b. In this example of the optical network 200 b in the ring networkconfiguration, subcarriers SC1-SC5 may be transmitted within the opticalnetwork 200 b. For example, a first subcarrier SC1 may be transmittedbi-directionally on bi-directional fibers between Node 1 and Node 5.Similarly, a second subcarrier SC2 may be transmitted bi-directionallyon bi-directional fibers between Node 5 and Node 4; a third subcarrierSC3 may be transmitted bi-directionally on bi-directional fibers betweenNode 4 and Node 3; a fourth subcarrier SC4 may be transmittedbi-directionally on bi-directional fibers between Node 3 and Node 2; anda fifth subcarrier SC5 may be transmitted bi-directionally onbi-directional fibers between Node 2 and Node 1.

FIG. 11B illustrates exemplary components of Node 5, comprising atransmitter 212, a receiver 226, a laser (LO), a de-mux component 902,and a combiner component 904. The de-mux component 902 may be configuredto split the subcarriers from the transmitter to direct the subcarriersto particular other nodes. In this example, the de-mux component 902 maysplit the subcarriers SC1 and SC2 from the transmitter 212 to directsubcarrier SC1 to Node 1 and subcarrier SC2 to Node 4. The combinercomponent 904 may be configured to combine the subcarriers entering Node5 to the receiver 226. In this example, the de-mux component 902 maycombine the subcarriers SC1 and SC2.

FIG. 12A illustrates an exemplary optical network 200 c having a hubconfiguration consistent with a further aspect of the presentdisclosure. The optical network 200 c may comprise a hub 920, a powersplitter 922, and two or more leaf nodes.

The hub 920 may have a transmitter 212 and a receiver 226. The hub 920may output a plurality of subcarriers, such as, for example, SC1-SC4, tothe power splitter 922. The power splitter 922 may supply a power splitportion of the plurality of subcarriers to one or more leaf node, suchas, for example, Leaf 1-4. Each Leaf Node may comprise a receiver 226that may receive all the subcarriers SC1-SC4 and that may output lessthan all of the data from the client data streams of all of thesubcarriers. For example, Leaf 1 may detect all of the subcarriersSC1-SC4, but may output the data from the data stream from one of thesubcarriers SC1. As described above regarding FIG. 7, the switch,blocking, or terminating circuit 865 in the receiver 226, may select oneof the subcarriers (or less than all of the subcarriers) and may outputdata from one of the client data streams 352 (or less than all of thedata streams).

FIG. 12B illustrates an exemplary optical network 200 d having a hubconfiguration consistent with a further aspect of the presentdisclosure. The optical network 200 c may comprise a hub 920, wavelengthselective switch (WSS) or de-mux component 930, and two or more leafnodes (Leaf 1-Leaf 4). The WSS or de-mux component 930 may output lessthan all of the subcarriers received from the hub 920 to a particularone of the leaf nodes. For example, the hub 920 may output a pluralityof subcarriers, for example, SC1-SC to the WSS or de-mux component 930,and the WSS or de-mux component 930 may output less than all of theplurality of subcarriers to the leaf nodes, such as, for example,outputting subcarrier SC1 to Leaf 1, while not outputting subcarriersSC2-SC4 to Leaf 1. Additionally, the leaf nodes may each, on a separatefiber, transmit a corresponding subcarrier back to the WSS or de-muxcomponent 930, which may detect all of the subcarriers SC-SC4 and outputthem to the hub 920.

FIG. 13 illustrates an exemplary optical network 200 e having a ring andhub network configuration consistent with a further aspect of thepresent disclosure. The optical network 200 d may include two or morenodes 202 interconnected with one another, such as exemplary nodes 202-1to 202-4, and further interconnected with at least one hub 206. The hub206 may comprise a transmitter 212 and a receiver 226 and may send andreceive a plurality of subcarriers, such as, for example, SC1-SC4. Eachof the nodes 202-1 to 202-4 on the ring may detect and output the dataassociated with a particular subcarrier of the plurality of subcarriers.A particular node may also transmit new data on the particularsubcarrier. The optical network 200 e may have bi-directional fibersbetween nodes 202 for bi-directional transmission. In someimplementations, a plurality of subcarriers may all be transmitted toall of the nodes 202, and each particular node 202 may extract and add aparticular subcarrier from the plurality of subcarriers. For example,subcarriers SC1-SC4 may be sent to node 202-1, which may extract datafrom subcarrier SC1 and add data to subcarrier SC1 and transmit all ofthe subcarriers SC1-SC4 on to node 202-2. Node 202-2 may receive all ofthe subcarriers SC1-SC4, and may extract data from subcarrier SC2 andadd data to subcarrier SC2 and transmit all of the subcarriers on tonode 202-3, and so on.

The below table illustrates a list of exemplary spectral efficiencies(that is, bits per unit spectrum) consistent with the presentdisclosure:

Spectral Max Efficiency Format RSNR RSNR-PS # Bins Fbaud InterpolationCap 11.64 64QAM: 9; 17.8 17 88 11.3 11:32 800 32QAM: 2 10.67 64QAM: 1;16.6 15.4 96 12.3 3:8 800 32QAM: 2 9.85 32QAM: 12; 15.3 14.3 104 13.313:32 700 16QAM: 1 9.14 32QAM: 4; 14.4 13.3 112 14.3  7:16 600 16QAM: 38.53 32QAM: 4; 13.5 12.5 120 15.4 15:32 600 16QAM: 11 8 16QAM 12.5 11.8128 16.4 1:2 600 7.11 16QAM: 5; 11.4 10.6 144 18.4  9:16 500 8QAM: 4 6.416QAM: 1; 10.2 9.7 160 20.5 5:8 400 8QAM: 4 5.82 8QAM: 10; 9.2 8.8 17622.5 11:16 400 QPSK: 1 5.33 8QAM: 2; 8.6 8.1 192 24.6 3:4 400 QPSK: 14.92 8QAM: 6; 7.9 7.5 208 26.6 13:16 300 QPSK: 7 4.57 8QAM: 2; 7.3 7.0224 28.7 7:8 300 QPSK: 5 4 QPSK 6 6 256 32.8 1:1 300

Accordingly, as noted above, a simplified and less expensive transmittermay be realized consistent with the present disclosure in which a laserand modulator may be employed to generate multiple subcarriers, wherebyeach of which may be detected and the client data associated therewithmay be output from receivers provided at different locations in anoptical network, for example. Improved network flexibility can thereforebe achieved.

Other embodiments will be apparent to those skilled in the art fromconsideration of the specification. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the invention being indicated by the followingclaims.

CONCLUSION

Conventionally, a plurality of lasers and modulators were necessary tocreate optical signals to carry a plurality of data streams. Inaccordance with the present disclosure, a plurality of subcarriers isgenerated from a single laser to carry a plurality of data streams, suchthat a lesser number of lasers and modulators are needed across anoptical network.

The foregoing description provides illustration and description, but isnot intended to be exhaustive or to limit the inventive concepts to theprecise form disclosed. Modifications and variations are possible inlight of the above teachings or may be acquired from practice of themethodologies set forth in the present disclosure.

Even though particular combinations of features are recited in theclaims and/or disclosed in the specification, these combinations are notintended to limit the disclosure. In fact, many of these features may becombined in ways not specifically recited in the claims and/or disclosedin the specification. Although each dependent claim listed below maydirectly depend on only one other claim, the disclosure includes eachdependent claim in combination with every other claim in the claim set.

No element, act, or instruction used in the present application shouldbe construed as critical or essential to the invention unless explicitlydescribed as such outside of the preferred embodiment. Further, thephrase “based on” is intended to mean “based, at least in part, on”unless explicitly stated otherwise.

What is claimed is:
 1. A transmitter configured to receive a pluralityof independent data streams, the transmitter comprising: a digitalsignal processor configured to provide outputs based on the plurality ofindependent data streams, the digital signal processor comprising aplurality of pulse shape filters corresponding to the plurality ofindependent data streams; digital-to-analog converter circuitryconfigured to selectively provide a first voltage signal output or asecond voltage signal output based on the outputs of the digital signalprocessor; a laser operable to output an optical signal; and a modulatoroperable to modulate the optical signal to provide a modulated opticalsignal including an optical subcarrier, which corresponds to one of theplurality of data streams, wherein, based on the first voltage signaloutput, the optical subcarrier has a first spectral width and, based onthe second voltage signal output, the optical subcarrier has a secondspectral width.
 2. The transmitter of claim 1, wherein the opticalsubcarrier is one of a plurality of optical subcarriers included in themodulated optical signal, each of the plurality of optical subcarriersbeing a Nyquist optical subcarrier.
 3. The transmitter of claim 1,wherein the optical subcarrier is one of a plurality of opticalsubcarriers included in the modulated optical signal, a number of theplurality of optical subcarriers is greater than a number of theplurality of independent data streams and wherein two or more of theplurality of optical subcarriers is associated with one of the pluralityof independent data streams.
 4. The transmitter of claim 1, wherein theoptical subcarrier is one of a plurality of optical subcarriers includedin the modulated optical signal, a first one of the plurality of opticalsubcarriers carries first data with a first symbol rate and a second oneof the plurality of optical subcarriers carries second data with asecond symbol rate different than the first symbol rate.
 5. Thetransmitter of claim 1, wherein the optical subcarrier is one of aplurality of optical subcarriers included in the modulated opticalsignal, a first one of the plurality of optical subcarriers and a secondone of the plurality of optical subcarriers each have a first datacapacity.
 6. The transmitter of claim 4, wherein the optical subcarriercarries data at a rate of 100 Gbit/sec.
 7. The transmitter of claim 1,wherein the optical subcarrier is one of a plurality of opticalsubcarriers included in the modulated optical signal, spectrallyadjacent ones of the plurality of optical subcarriers being separatedfrom one another by a variable frequency spacing.
 8. The transmitter ofclaim 1, wherein the spectral width is wider than the first spectralwidth.
 9. The transmitter of claim 1, wherein the optical subcarriercarries information for clock recovery.
 10. The transmitter of claim 1,wherein the optical subcarrier is one of a plurality of opticalsubcarriers, each of which is modulated in accordance with the samemodulation format.
 11. The transmitter of claim 1, wherein the firstvoltage signal output is indicative of a first modulation format and thesecond voltage signal output is indicative of a second modulation formatdifferent than the first modulation format.
 12. The transmitter of claim11, wherein the first modulation format is one of BPSK, QPSK, and m-QAM,where m is an integer, and the second modulation format is another oneof BPSK, QPSK, and n-QAM, where n is an integer different than m. 13.The transmitter of claim 11, wherein the first modulation format is oneof BPSK, QPSK, and m-QAM, where m is an integer, and the secondmodulation format is an intensity modulation format.
 14. The transmitterof claim 1, wherein the plurality of pulse shape filters operate onfrequency domain signals.
 15. An optical network, comprising: atransmitter configured to receive a plurality of independent datastreams, the transmitter comprising: a first digital signal processorconfigured to provide outputs based on the plurality of independent datastreams, the first digital signal processor comprising a plurality ofpulse shape filters corresponding to the plurality of independent datastreams; digital-to-analog converter circuitry configured to selectivelyprovide a first voltage signal output and a second voltage signal outputbased on the outputs of the first digital signal processor; a laseroperable to output an optical signal; and a modulator configured tomodulate the optical signal to provide a modulated optical signalincluding an optical subcarrier, which corresponds to one of theplurality of data streams, wherein, based on the first voltage signaloutput, the optical subcarrier has a first spectral width and, based onthe second voltage signal output, the optical subcarrier has a secondspectral width; and a receiver, comprising: circuitry configured toreceive the optical subcarrier and output analog signals; and a seconddigital signal processor configured to output said one of the pluralityof independent data streams based on the analog signals.
 16. The opticalnetwork of claim 15, wherein the optical subcarrier is one of aplurality of optical subcarriers included in the modulated opticalsignal, the optical network further comprising: one or more opticaladd-drop multiplexer (OADM) configured to drop one or more of theplurality of optical subcarriers.
 17. A transmitter configured toreceive a plurality of independent data streams, the transmittercomprising: a digital signal processor configured to provide outputsbased on the plurality of independent data streams; digital-to-analogconverter circuitry configured to selectively provide a first voltagesignal output and a second voltage signal output based on the outputs ofthe digital signal processor; a laser operable to output an opticalsignal; and a modulator operable to modulate the optical signal toprovide a modulated optical signal including an optical subcarrier,which corresponds to one of the plurality of independent data streams,wherein, based on the first voltage signal output, the opticalsubcarrier has a first spectral width and, based on the second voltagesignal output, the optical subcarrier has a second spectral width.